This study aimed to clarify the significance of cluster of differentiation 9 glycoprotein gene expression in human parotid gland tumours.

We retrospectively analysed immunohistochemical staining for cluster of differentiation 9 glycoprotein in parotid gland tumours.

Cluster of differentiation 9 glycoprotein was consistently detected in the normal parotid gland. Regarding benign parotid gland tumours, cluster of differentiation 9 glycoprotein was present in 13 of 18 pleomorphic adenomas, in all Warthin tumours tested (21/21) and in all cases of basal cell adenoma tested (four of four). In contrast, positive staining for cluster of differentiation 9 glycoprotein was less often observed in malignant parotid tumours. Cluster of differentiation 9 glycoprotein was present in 11 of 14 mucoepidermoid carcinomas, in two of five acinic cell carcinomas and in two of five adenoid cystic carcinomas.

There was a statistically significantly reduced expression of cluster of differentiation 9 glycoprotein in malignant parotid gland tumours, compared with benign parotid gland tumours (p < 0.05). These results suggest that a low level of cluster of differentiation 9 glycoprotein expression in parotid gland tumours may be associated with malignancy.